A plasma display generally comprises two tiles, leaving between them a space filled with a discharge gas, and at least two arrays of electrodes which intersect, these generally being deposited on each of the tiles; by applying a potential difference between an electrode of the first array and an electrode of the second array, a discharge is created in the gas between the tiles at the intersection of these electrodes; this discharge emits ultraviolet radiation which is converted, by the phosphors partially covering the internal surface of the tiles, into visible radiation.
A plasma-addressed liquid-crystal display (PALCD) is generally formed by superposing a plasma addressing panel and a liquid-crystal panel, and also includes at least two arrays of electrodes which intersect; the plasma addressing panel generally comprises, as above, two tiles leaving between them a space filled with a discharge gas; by applying a potential difference between an electrode of the first array and an electrode of the second array, a discharge is created in the gas at the intersection of these electrodes; this discharge is equivalent to the closing of a switch and allows a potential difference to be selectively addressed at the terminals of the liquid-crystal cells located opposite this discharge.
A field emission display (FED) also comprises two tiles leaving between them an empty space intended for the path of electrons emitted by the field-effect cathodes towards the anode; this empty space contains in fact a gas under very low pressure.
All these displays therefore comprise two tiles leaving between them a space containing a gas; the tiles are made of rigid material in order to withstand the difference between the external pressure and the internal pressure; these tiles are generally made of electrically insulating materials; thus, these tiles are generally made of glass, glass-ceramic or ceramic.
With reference to FIG. 3, the manufacture of such displays 10 comprising two tiles 4 and 5, leaving between them a space 7 containing a gas, generally comprises the following steps:                manufacture of the first tile 4 and second tile 5, one of the tiles, 4, being provided with a pumping orifice 6;        assembly of the tiles 4, 5, so as to be mutually parallel and separated by a distance sufficient to leave between them a space 7, by applying a sealing compound 61 around the perimeter of the tiles;        fitting of a pumping and sealing tube 1 into the pumping orifice 6, by applying a sealing compound 62 between the walls of the tube and those of this space around the orifice;        pumping-out of the gas contained in this sealing space 7 through the pumping tube 1;        sealing of this space 7 by closing off the pumping tube 1.        
The thickness of the space 7 left between the tiles 4 and 5 is in general approximately constant and tailored to the operation of the display 10.
As sealing compounds 61, 62, it is general practice to use a glass sealing compound; it is then necessary to carry out a heat treatment to vitrify this joint, before the pumping step, so as to form seals 61′, 62′.
During the pumping step, the display is generally heated in order to facilitate the absorption of the occluded gases in the space between the tiles.
In the specific case of plasma displays, to be able to obtain plasma discharges between the tiles this space must contain a discharge gas, of suitable composition and pressure; the manufacture of the display therefore furthermore includes, after pumping and before sealing, a step of filling the display with the discharge gas through the same tube 1 used previously for the pumping.
To perform these operations, it is particularly important that the pumping tube, as fitted onto the display, be able to withstand the mechanical shear and compressive stresses; this remains true for the rest of the operations for manufacturing the display, since the pumping and sealing tube remains fastened to the display and must be able to withstand accidental impact during subsequent handling.
Such a pumping, sealing and, where appropriate, filling tube 1 is generally called a stem tube.
Document GB 2 261 320 discloses a stem tube provided with metal shoulder means which are intended to bear on the tile around the periphery of the pumping orifice and onto which a glass pipe is fitted in order to connect the pumping means and to seal the display; this pipe does not penetrate the hole in the tile.
So as to be able to easily and rapidly position the pumping tube 1 and, in this case, so as to fit its end 21 into the pumping orifice 6, whatever the clearance between the tube and the orifice (difference in diameters), and so as to facilitate the operation of sealing between this tube and the orifice by means of the seal 62′, document FR 2 796 490 discloses a stem tube provided with shoulder means 3 which are intended to bear on the tiles 4 around the periphery of the pumping orifice 6; according to that document, these shoulder means have a plane shoulder surface 31, generally perpendicular to the axis of the tube, intended to bear against the external surface 41 of the tile 4 located around the periphery of the pumping orifice 6, and thus make it easy for the axis of the end 21 of the tubular pipe 2 to be made coincident with the axis of the pumping orifice 6, thereby making it easier to fit the stem tube.
When this shoulder surface 31 extends continuously, radially from the tube and peripherally around the tube, for example when it forms a flat disc as shown in FIG. 1, these shoulder means facilitate the operation of sealing between the walls of the tube and those of the space between the tiles: the sealing compound 62 is then applied directly to this surface 31, as shown in FIG. 2; if the shoulder surface is wide enough, such an embodiment therefore facilitates the sealing operation.
Referring to FIGS. 5 and 6, for the pumping, and where appropriate filling, step, the other, downstream end 22 of the tube 1 is connected to a pumping and filling installation (not shown) via a connection end-piece 8, 8′; the connection may be made, for example, either by bonding in the case of the end-piece 8 of FIG. 5 or by removable connection means 81 in the case of the end-piece 8′ of FIG. 6.
There is an advantage in using a glass pipe 2 as it makes the subsequent sealing step easier; this is because, after the pumping, and where appropriate filling, step, all that is then required is to melt the glass of the pipe 2 at the sealing point S in order to seal the space 7 between the tiles; the connection end-piece 8, 8′ can then be easily cut off or removed.
However, a glass pumping tube is in general more difficult to position correctly at the orifice 6 by means of automatic machines; this is because the tolerances at the end 21 and at the shoulder 3 on the tile's 4 side may, if the material is glass, pose a problem in positioning it rapidly and effectively.
Moreover, a glass part is always tricky to handle with automatic machines; in the case of a moulded glass pumping tube, like that shown in FIG. 7, this part generally has a conical outer surface 29 in order to facilitate moulding, which makes it even more difficult to handle precisely.
The object of the invention is to mitigate the aforementioned drawbacks.